1. Field of the Invention
The embodiments described herein relate to a multi-detector inverse fan beam x-ray diffraction imaging (MIFB XDI) system and, more particularly, to an x-ray source suitable for use with an MIFB XDI system.
2. Description of Related Art
Known security detection systems are used at travel checkpoints to inspect carry-on and/or checked bags for concealed weapons, narcotics, and/or explosives. At least some known security detection systems include x-ray imaging systems. In an x-ray imaging system, an x-ray source transmits x-rays through an object or a container, such as a suitcase, towards a detector, and the detector output is processed to identify one or more objects and/or one or more materials in the container.
At least some known security detection systems include a multi-detector inverse fan beam x-ray diffraction imaging (MIFB XDI) system. MIFB XDI systems use an inverse fan-beam geometry (a large source and a small detector) and a multi-focus x-ray source (MFXS). At least some known x-ray diffraction imaging (XDI) systems provide an improved discrimination of materials, as compared to that provided by other known x-ray imaging systems, by measuring d-spacings between lattice planes of micro-crystals in materials. Further, x-ray diffraction may yield data from a molecular interference function that may be used to identify other materials, such as liquids, in a container.
However, with at least some XDI systems that incorporate an MFXS in the inverse fan beam geometry a distribution of scatter signals across the object under investigation, e.g., a suitcase, may be significantly non-uniform. The non-uniform distribution of scatter signals may occur when a spatial extent of the MFXS, a lateral width of the suitcase and a spatial extent of the coherent x-ray scatter detector array are all comparable to one another. An example of such non-uniformity is shown in FIG. 1. Referring to FIG. 1, the MFXS (not shown) and the detector array (not shown) are both equal in width to a horizontal width of a container, such as a suitcase 5 positioned within an examination area 6 of a conventional MIFB XDI system. X-ray beams that are emitted by the MFXS and transmitted through areas, each designated by reference number 7, are detected only by one detector, whereas x-ray beams that are emitted by the MFXS and transmitted through areas each designated by reference number 8 are detected by two detectors, and these areas are relatively large in extent.
In order to achieve a more uniform coverage of the object, it is desirable that the MFXS is smaller than the object width. As a result, a group of corresponding x-rays, referred to herein as an inverse fan beam bundle of x-rays, from the MFXS arriving at each detector is fairly narrow (in a horizontal direction) and approximates a “pencil beam” that sweeps across the object from a beginning of a scan to an end of the scan.